The invention is based on a hydraulic dual-circuit brake system with an anti-skid system (ABS) and traction control (ASR) for motor vehicles.
In a known dual-circuit brake system of this type (German Patent Document 38 16 073 A, now U.S. Pat. No. 4,900,102), a return pump has a third pumping element acting as a precharge pump, which is disposed between a charging valve embodied as a hydraulically controlled 2/2-way valve and a pumping element associated with the brake circuit of the driven wheels. The control inlet of the charging valve is connected to the brake circuit outlet of the master brake cylinder. When there is control pressure at the control inlet, the charging valve is switched over to its blocking position. During traction control the reversing valve is reversed and thereupon disconnects the brake circuit from the brake circuit output of the master brake cylinder, and connects the brake circuit to the brake circuit outlet of the master brake cylinder via the pressure limiting valve. The third pumping element now supplies the following pumping element of the return pump, which generates a high braking pressure that is present at the inlet to the control valve. This brake pressure is fed via the control valves, embodied as 3/3-way magnet valves, into the wheel brake cylinders of the driven wheels, which are slowed down as a result. If only one driven wheel is spinning, then the control valve associated with the outlet channel for the wheel brake cylinder of the nonspinning driven wheel is moved to its middle position, so that no brake pressure can be built up in the wheel brake cylinder of the driven wheel that is not spinning.